Process for production of alkali metal chlorates, and more particularly potassium chlorate



June 23, 1942. s OSBORNE ETAL 2,287,061

PROCESS FOR PRODUCTION OF ALKALI OMETAL CHLORATES, AND

MORE PARTICULARLY POTASSIUM CHLORATE Filed April 15, 1940 Mofher Liquorand Wash Wafer afar 25 2/' 22 g A A A Slurry 2 v v *G Was/l W 9 2 25,...l Crysfalll'zer Dr or 27 28 Y 29 y l ENTOR- RM 5m BY M A Patented June23, 1942 PROCESS FOR PRODUCTION OF- ALKALIv METAL CHLORATES, AND MOREPARTICU- LARLY POTASSIUM CHLORATE Sidney G. Osborne, St. Davids,Ontario, Canada,

and Robert 'B. Lowry and Walter S. Beanblossom, Niagara Falls, N. Y.,assignors to Hooker Electrochemical Company, Niagara Falls, N. Y., acorporation of New York Application April 15, 1940, Serial No. 329,738

Claims. I (01. za-ss) Chlorates are produced by chlorination of alkalimetal and alkaline earth hydroxides and salts of weak acids, such as thecarbonates. A

It has been proposed to produce chlorates from alkali-chlorine cellefliuent by reacting it directly with chlorine, but in that case anevaporation step is necessary to remove the sodium chloride in theeflluent and formed by the reaction and recover the product. The cost ofthis evaporation has prevented this process from ever becomingeconomically practicable.

Chlorates may of course be produced by evaporating down such celleffluent to separate out the caustic alkali and reacting this withchlorine, but in this case, as in the preceding, the cost of theevaporation has proven to be prohibitive.

Sodium and potassium chlorate are also produced directly in electrolyticcells by allowing the chlorine evolved on the anode to mingle with thecaustic soda produced at the cathode. Hypochlorite is formed first, andthis breaks down into chlorate and chloride. The hypochlorite andchlorate are both unstable and powerful oxidants. It is thereforenecessary to operate these cells .below 70 C., and even at thistemperature the attack on the electrodes is severe. The cathode, if ofsteel, is liable to rust rapidly, particularly in any recesses wherecirculation is not good. Even the graphite anodes are rapidly consumedby oxidation. The hydrogen evolved is found to be contaminated by carbondioxide. Moreover, under certain conditions it may contain enough oxygento constitute an explosive mixture. The reaction between chlorine andcaustic soda takes place largely in the presence of nascent hydrogenwhich reduces some of the product into salt and water. The graphitealso, being a reducing agent, breaks up some of the product. Oxidationof the steel accounts for still more. For these and other reasons, theyield of such cells, based upon current consumed, is seldom better than80%. By

- contrast, the yield or current efiiciency of the highly developedalkali-chlorine diaphragm cells is in general 90% or better. In the caseof the cell illustrated in U. S. Patent No. 1,866,065, the currentetficiency is ordinarily 95%. It is highly desirable therefore to beable to utilize caustic soda and chlorine produced in such cells forproduction of chlorates.

The crude product or eliluent from alkali-chlorine cells is in general aliquor containing about 9 /2% NaOH and 13 NaCl. The cell of the patentreferred to, however, produces a crude effluent containing about 11%NaOH and 15%% NaCl. This increased concentration is made pos sible byits high efiiciency and the fact that this cell is supplied with brinewhich is saturated at 70 C. by theprocess of the U. S. Patent No.2,173,986, therefore contains about 320 grams of NaCl per liter, whereasin general electrolytic alkali-chlorine cells are supplied with brinecontaining about 290 grams NaCl per liter.

It is known that sodium hydroxide may be converted to sodium carbonateor bicarbonate by reaction with carbon dioxide. In the case of theelectrolytic cell illustrated in Hargreaves-Bird British Patent No.18,039 of 1892, this is accomplished by admitting steam and gasescontaining carbon dioxide directly to the cathode compartment of thecell. This compartment becomes completely filled with an atmosphere ofthe gases, so that the cell eflluent containing sodium hydroxide comesinto contact with the carbon dioxide as fast as it percolates throughthe diaphragm. The efliciency of such a cell is seldom better than 88percent and the carbonation product is in solution. In the cell ofPatent No. 1,866,065, the diaphragm is submerged, one side being incontact with the electrolyte and the other with the efiluent. This isone'of the reasons for the high efliciency of the cell. Obviously itwould be impracticable to fill the anode compartment of this cell withan atmosphere of CO2. Nevertheless it is desirable to be able to use acell of this eflicient type for production of chlorate. It would ofcourse be possible to bubble carbon dioxide through the cathodecompartment of such a cell, but since the cathode compartment is notdesigned for this purpose the absorption of CO2 and conversion ofhydroxide to carbonate would be incomplete; moreover, the hydrogenevolved in the cathode compartment of such cells, which is a valuable byproduct, would in that case be contaminated with CO2 and its valuegreatly reduced.

We have found tht if effluent from such a cell is treated with CO2 in aneflicient absorption apparatus, more or less of the resulting sodiumcarbonate or bicarbonate forms a precipitate in the cell eiiluent,depending upon the conditions, and may be filtered out, thus separatingthe carbonate from the chloride without the necessity of any evaporationstep. This precipitate is especially efiicient in the case of the cellof Patent No. 1,866,065, because of the fact that the eiiluent from thecell is more concentrated with respect to NaOH and NaCl than is theeffluent from such cells in general. It is also particularly true if thecarbonation of the cell efliuent is carried beyond the sodium carbonatestageto the 'point at which the product is sodium bicarbonate,

since the latter is much less soluble than the former. After thecarbonate or bicarbonate has been filtered out, the filtrate is ofcourse recycled to the electrolytic cells. The carbonate or bicarbonate,after its removal from the cell eiliuent, may then. be chlorinated toproduce sodium chlorate and chloride and the carbon dioxide evolved bythis chlorination recycled to produce 4 more carbonate or bicarbonate.In this way we are able to make use or the highly efllcientalkalichlorine diaphragm cell referred to, without incurring the cost ofevaporation otherwise necessary to separate the hydroxide, carbonate orbil0 carbonate from the chloride, or the chlorate from the chloride ifthe cell eflluent be directly treated with chlorine, and withoutcontaminating the valuable hydrogen produced in the cell with C02. Atthe same time we avoid the waste of carbon dioxide incident to producingthe carbonate or bicarbonate as an end product, and chlorinating it inanother plant.

The composition of the cell eilluents referred to above may be expressedas follows:

Weight percent Mols NIOH 9% to 11 2 2 N801. 13% to 15% I. 1.92

mo 71 to ma es 20.1

It will therefore be seen that NazCO: is an intermediate product in theproduction of NaHCOa, the latter requiring twice as much 00:.

After completion of the carbonation in accordance with Reactions 1 or 2some of the carbonation product is in the form of a precipitate and someof it in solution. The solution is then brought to saturation withrespect to NaCl, whereupon more carbonation product is precipitated.This is then filtered out.

Example I.-1l per cent NaOH unsaturated cell eilluent was carbonated toNazCOi in accordance with Reaction 1. The composition after carbonationwas as follows: 7

This represents a yield of NazCO: and NaHCO: amounting to 82.9 percentof the theoretical yield, based upon current supplied to the cell andassuming the cell efllciency at percent, or a yield 65 of 14.22 percentin the precipitate.

This example shows that when the cell eilluent containing 11 percentNaOH is carbonated to NazCO: only a minor part of the product isprecipitated, which explains why the Hargreaves- Bird cell yields aproduct that is entirely in solution, as stated above.

Example II.11 percent NaOH solution was carbonated to NazCO-i inaccordance with Re- .1

action 1 and saturated by adding NaCl. The composition after carbonationwas as inflows:

Solids Filtrate No.00. nai NallC0|.. a0 0 m a 000 o action 2 andsaturated by adding NaCl. The composition after carbonation was asfollows:

Solids This represents an overall yield of NaaCO: and NaHCOs amountingto 90.6 percent of the theoretical yield, based on the current suppliedto the cell, assuming the efliciency of the latter as before, or a yieldof 17.4 percent in the precipitate. A comparison of this yield with thatof the preceding example shows that it is preferable to carbonate to thebicarbonate stage.

Instead of bringing the solution to saturation after carbonation as inExamples 11 and m it may be saturated before carbonation. The resultsare then as follows:

Example IV.11 percent NaOH solution saturated by adding NaCl-was thencarbonated to NaHCO: in accordance with Reaction 2. The

composition after carbonation was as follows:

Bollds Filth No.00: 37. M 1. 57 NnHCOa m 89 9. 77 NlCl 29. 60 2%. (I)H10 1, (II). (I)

Solids Filtrate This represents a yield of NazCO: and NaHCO:

urated by adding NaCl was carbonated to\lo NaI-ICQ in accordance'withReaction 2 under a gauge pressure of 2 0. mo! mercury. The compositionafter carbonation was as follows Solids Flltrate This represents a yieldof NaaCOa and NaHCOa amounting to 96.0 percent of the theoretical yield,assuming the cell efficiency at .95 as before, or a yield of 92.7percent in the precipitate. A comparison of this result with that ofExample IV shows that a slight pressure assists the absorption of CO2sufficiently to raise the yield from 89.0 to 92.7 percent.

In the foregoing examples the carbonated liquor was in every case cooledto C. and allowed to stand overnight before filtration.

In the case of Example III, IV, V, and VI, in which carbonation wascarried to bicarbonate, the carbonation products in the filtrate arenegligible. In the case of Ex mp I nd II t ey 3 are not negligible andordinarily the precipitation of carbonate in these examples would not beconsidered complete enough to justify commercial operation on thisbasis. However, in an electrolytic alkali-chlorine installation thereare other uses for sodium carbonate for which a filtrate such as thoseof Examples I and II can be used just as it is. For example, if thereare a number of cell circuits and some of them are not used forproduction of chlorate, the filtrate can be returned to the brine systemfor the whole plant, in which case the carbonate will serve the usefulpurpose of precipitating lime and magnesium from the brine, for whichpurpose it is otherwise necessary to supply carbonate from othersources.

The batch chlorination of sodium carbonate, like the carbonation ofcaustic soda, proceeds by two stages, as follows: ZNazCOs-i-HzO-l-Clz(3) NaCi'O+NaCl+2NaHCOs NaClO+NaCl+2NaHCOa+Clz (4) The water absorbed inReaction 3 is therefore given back in Reaction 4. However, during thefirst stage represented by Reaction 1 there is a thickening of thereaction mixture. During the second stage represented by Reaction 4there is much evolution of CO: and this not only causes foaming butcarries ofi more water than is formed in the reaction, so that there isa further thickening. This foaming is objectionable as it necessitatesdiluting the reagents or providing a larger foam space in the reactor.We have found that by adding the sodium carbonate continuously or inincrements during the chlorination the evolution of CO2 is'spread outover a longer period and the foaming is reduced; consequently thethickening of the reaction mixture at any moment is likewise reduced.This enables us to finish with a higher proportion of sodium carbonate,which is of advantage in later separating out sodium chlorate, as weshallpresently show, and also to chlorinate a greater quantity ofcarbonate in a reactor of given capacity. Reactions 3 and 4 may becombined as follows:

The NaClO of these equations of course breaks down into NaClOi and NaCl,so that Equation 5 may be written:

Since sodium carbonate is converted to sodium bicarbonate during thechlorination, it is immaterial from the point of view of the flnalresult whether the chlorination start with the carbonate or bicarbonate.Although, if this process is to start with electrolytic caustic soda,the yield is much higher if we carbonateto bicarbonate, the latter partof the process, from the chlorination step onward, is not limited toelectrolytic caus-e tic soda, but may make use of natural or othersodium carbonate. Therefore we do not wish the process to be limited toeither carbonate or bicarbonate.

The sodium chlorate produced by Reaction 6 may then be converted topotassium' chlorate by reaction with potassium chloride as follows:

Weight percent Mols K010 4. 3. NaCl 24. 9O 42. 6 H 0. 70. 25 3'36. 0

This mother liquor is saturated with respect to KClO3 and almostsaturated with respect to NaCl at 10 C., which is a satisfactorycrystalllzati-on temperature. To this liquor sodium carbonate is added,preferably in the proportion of about 60 grams per liter. Whensufiicient chlorine has been added to chlorinate substantially all thissodium carbonate another equal weight of sodium carbonate is added. Thisis repeated until a total of 240 grams have been added per liter of theoriginal mother liquor.

If all the sodium carbonate were added at the start the composition ofthe reaction mixture chlorinated would therefore be as follows:

Weight percent M 015 Reaction 6 as actually carried out shouldthereforebe written as follows:

It will be noted that in Reaction 8 the water is reduced by evaporationin the proportion of from about 64 mols to about 55 mols. This is veryimportant, as will be shown later.

If it is desired to chlorinate sodium bicarbonate instead of sodiumcarbonate the analogous reaction is as follows:

It will be noted that the products of Reaction 9 are'slightly moredilute than those of Reaction 8, due to re-formation of 3 mols of 11:0.However, since twice as much CO: is evolved in Reaction 9 as in Reaction8 this extra quantity of water may be easily carried 01! during thereaction.

In this case the final quantity of bicarbonate 4 added is of courselimited to about 192.5 grams per liter of mother liquor.

The NaClO: of Reaction 8 or 9 is then converted to K010: and NaCl byreaction with KCl as During the chlorination the temperature of courserises. At its conclusion the temperature is 50 to 70 C. The solubilityof KClO.| rises rapidly with temperature, while that of NaCl increasesonly slightly. Therefore at 60 C. the K010i formed by the reaction isall or mostly in solution, while the NaCl formed is mostly aprecipitate. The NaCl formed may therefore be filtered out. The cake ofsalt is then washed as hereinafter described, finishing with freshwater, and recycled to the start of the process, diverting to thecarbonation as much salt as may be necessary to saturate the celleiliuent.

It should be noted that when the final product is KClO: no sodium leavesthe system. Also that KCl brings into the system all the chlorine thatleaves as KClOa. Therefore there is no need to add make-up NaCl, exceptto replace minor losses. It is necessary, however, to supply water tothe start of the process to furnish the oxygen of the KClOs.

The specific gravity of the filtrate at 60 C. is 1.271 and itscomposition is as follows:

Weight per cent KC101 14.26 Nafl 23.10 H2O 62.64

In order to bring the filtrate slightly below saturation with respect toNaCl a small quantity of water or solution saturated with respect toKClOa but low in NaCl, obtained from the washing of the final product ashereinafter to be described, is now added to the filtrate. After thisdilution the composition of the filtrate is approximately as follows:Weight per cent KClOs--- 14.1 NaCl 22.7 H 63.2

tity that is required to be added Just prior to crystallization butmaybe so calculated as to make up all the water carried out by the CO:in the chlorination reaction. This will be more than is required to beadded Just prior to crystallization. A part of this is therefore used towash the cake of salt on the filter as above. The balance is returned tothe chlorination reaction. This tends to balance the water on the twosides of Equations 8 and 9. v

The quantity of wash water added to the filtrate just prior tocrystallization affects the purity of the product with respect tocontaminating NaCl, as follows:

The percentage of NaCl in the product may then be further reduced to 0.4or less by washing and centrifuging the crystals. From this it will beseen'that the process results in a product very low in NaCl. I

The quantity of water that can be used to wash the produce and bereturned to the process without progressively increasing the quantity ofwater in the process or resorting to vacuum crystallization, and hencethe quality of the product, depends directly upon the water removed inthe chlorination reaction. This is a fraction of the temperature atwhich this reaction is carried on. For this reason we carry on thereaction at the highest practicable temperature, namely 50 to 70 C., andpreferably nearer the upper 01' these limits.

Hall the carbonate were added to the mother liquor in one installmentand no wash water returned during chlorination, the concentration of thereaction mixture would increase appreciably and it would be necessary toadd fresh water in order to be able to carry it on. Hence it is veryimportant to add the carbonate by increments not over one-quarter of thetotal at one time and return the wash water before the chlorination.

The CO: from Reaction 8 or 9, as the case may be, is of course recycledto Reactions 1 or 2 respectively.

Example VII.--The chlorinator was charged with mother liquor containingthe following:

The products of the chlorination yielded 14.37 pounds of finishedcrystalline product, corresponding to a net yield of 93.5 percent of thetheoretical yield of KClOa.

Referring to the fiow sheet:

I is an electrolytic alkali-chlorine diaphragm cell of the type referredto. I is a reservoir for electrolyte which is supplied to the cellthrough pipe 3. Hydrogen leaves the cell through pipe 35. As thishydrogen does not enter into the present process it may be considered asa byproduct. Chlorine leaves the cell through pipe ll. 4 is a pipethrough which the cell eiiiuent flows into funnel 5, whence it isconducted through pipe 8 to carbonator I. i

Since the cell preferably operates continuously and the succeeding stepsofthe process may be by batches. storage for cell eiiiuent (not shown)may be provided between cell i and carbonator I.

Into carbonator I, which may be an absorption tower, CO: from pipe 8 isintroduced near its bottom. The product of this reaction, being of lowsolubility in brine, is precipitated, while the NaCl remains insolution.

The cell eiiiuent, containing approximately 11 percent NaOH and /2percent NaCl, is not a saturated solution. It should therefore bebrought up to saturation by adding more NaCl, either before or aftercarbonation. As this salt is more eifective in increasing theprecipitation of carbonation product if added before carbonation (asshown by comparison of the yields obtained in Examples III and IV) it ispreferably added before carbonation.

The carbonate and brine are then passed through pipe 9 to filter it,which may be of the rotary or other type. In this filter the brine isremoved to the interior, whenc it may be returned through pipe H toreservoir 2 for repassage through the cell. The salt necessary tosaturate the cell efiiuent' is introduced at 32; The solids from filterID are transferred through pipe or chute E3 to chlorinator II where theyare brought into contact with mother liquor derived from thecrystallizing, centrifuging and washing of the final product, introducedthrough pipe 26.

Chlorine from the cell is then introduced through pipe it to chlorinatorM at a point near its bottom. As the chlorination reaction is onlyslightly exothermic, the temperature within the chlorinator is keptbetween 50 and 70 C., by any convenient means (not shown) In chlorinatorl4 carbon dioxide is liberated'in accordance with Reactions 8 or 9. Thisgas is returned through pipe 8 to carbonator I, there to serve asreagent in Reaction 1 or 2 as the case may be. The moisture carried awayfrom chlorinator M by this gas is condensed and removed in dephlegmator30 and pipe 3|, to be later replaced by wash water from the washing ofthe final product in the centrifuge, as later described.

Before, during or after chlorination if the product is to be K0103, KC]is likewise introduced into chlorinator M, as through pipe Hi.

The mother liquor and wash water returned through pipe 26, aresufilcient to take into solution the chlorate but not the chlorideformed by the reaction, at the temperature of reaction, namely 50 to' 70C. Therefore inorder to remove the chloride from the chlorate a simplefiltration is all that is necessary. vAccordingly, the products of thereaction are transferred through sluice ill to filter 38, which may beof the rotary type as shown. This filter separates out the solid sodiumchloride which is then transferred through conduit 59, which may bea'conveyor, back to the process. As much of this salt as may benecessary to saturate the cell eflluent is diverted through conduit 32to carbonator I.

The balance is returned to reservoir 2. Water to lake this into solutionis introduced through pipe The quantity of KCl introduced at it shouldpreferably be less than sufficient to convert all the NaClOa to K0103. Asmall quantity of NaClO-z will then go alon with the KClOa and, beingmuch more soluble, will remain in the mother liquor. The possibility ofKCl finding its way back to the cell through conduit I9 is thus avoided.The filtrate from filter I8 is transferred through pipe 20 tocrystallizer 2!. After addition of the necessary water to inhibit thecrystallization of NaCl the filtrate is cooled to 10 C. It may also beseededwith crystals of chlorate. These crystals and mother liquor aretransferred through conduit 22, which may be a, conveyor, to centrifuge23. Here the crystals are separated from the mother liquor bycentrifuging and then washed with water introduced through pipe 24. Apart of the wash water from centrifuge 23 is passed back through pipe 25to crystallizer 2|. A portion of the mother liquor is recycled throughpipe 33 to wash the cakes of salt on filter l8. Fresh water may likewisebe introduced through pipe 34 to cleanse this cake of salt of motherliquor more completely. The remainder of the wash water, together withthermother liquor, is passed through pipe 26 back to chlorinator H, asstated above, there to serve as a menstruum for the chlorinationreaction and to take the chlorate into solution. The water introduced at24 plus that introduced at 34 should be sufiicient to replace thatremoved at 3|, but no more. The

solid washed crystals from centrifuge 23 are then transferred throughconduit 21, which may be a conveyor, to a recrystallizer (not shown) andthence to dryer 28 or directly to dryer 28, whence they are delivered topacking drum 29 for the market.

Storage (not shown) may be provided between chlorinator I4 and filter I8also for wash water and mother liquor in pipes 25 and 26 respectively.

The several reactions of the process may be summed up as follows:

From Equation 11 it will be seen that five sixths of the sodium thatcomes from the electrolytic cell as NaOH is recycled as NaCl and onlyone-sixth requires to be replaced. If the product is KClOa, as in theflow sheet, this sodium is replaced by the potassium of the K01introduced at 16 and this KCl also brings into the systemthe chlorine ofthe KClOa. The oxygen of the KClOsiS supplied by water introduced to thecell at l2. If the productwere NaClOa it would be necessary tointroduceto the cell one part of. NaCl for each NaClOs in the finalproduct.

Referring back to Examples VI and VII, it

will be seen that our process is capable of a yield of 95 percent in theelectrolytic cell, 97.6 percent in the carbonation step and 93.5 percentin the chlorination and finishing steps, an overall yield,

from current supplied the cell to finished crystalline product, of over86 percent. The yield of the best electrolyte chlorate cells is seldombetter than 80 percent of NaClO: in the liquid cell eiliuent and '75percent, based upon finished crystalline product. By taking advantage ofthe most efficient type of alkali-chlorine cell and the most efiicientcarbonation and chlorination steps that we have been able to work outafter careful reor our knowledge and belief, been an unavoidable featureof all previous processes; and we are thus enabled to save the attendantcosts and losses of product. These however, are not the only advantagesof our process. In the varying conditions of the chemical industry thedemand for any given product'is liable to change quickly. Anelectrolytic chloratecell installation is capable of producing nothingelse and the demand for this product is quite variable and seasonal;whereas, although the demand for caustic soda is variable this productis basic to many industries. By our-- process, when caustic soda is inmore demand than sodium carbonate. as is normally the case. we canproduce chlorate from the latter; and when the supply of caustic sodaexceeds the demand we can utilize the electrolytic cell installation toproduce chlorate. Thus the installation of electrolytic cells may beused for either one of two alternative products and the heavy investmentwhich it represents is better safeguarded. Our process therefore has theadvantage of flexibility, which is always an important consideration inthe chemical industry.

We claim as our invention:

1. The process for production of alkali metal chlorate from electrolyticcaustic soda-chlorine cell eiiiuent with avoidance of evaporation ofwater therefrom which comprises electrolyzing sodium chloride in anelectrolytic cell, carbonating the caustic alkali out of the resultingcell eiliuent as far as practicable to sodium bicarbonate, filtering outthe resulting precipitated carbonation product, recycling the filtrateto the anode compartment of the electrolytic cell, introducing saidcarbonation product into an aqueous menstruum in quantity sufiicient totake into solution at 50 to 70 C. most of the chlorate but only a littleof the chloride which may be produced by chlorinating said carbonationproduct, chlorinating said carbonation product to produce thecorresponding chlorate, recycling the resulting carbon dioxide to thecarbonation step,

filtering out chloride and recycling it to the anode compartment of theelectrolytic cell, crystallizing out and removing chlorate from thefiltrate, recycling the mother liquor to the chlorination step to serveas menstruum for said carbonation product and introducing into thesystem make-up water and chloride to supply the oxygen and chlorinewithdrawn from it with the product.

2. The process for production of sodium chlorate from electrolyticcaustic soda-chlorine cell efliuent with avoidance of evaporation ofwater therefrom which comprises electrolyzing sodium chloride in anelectrolytic cell, carbonating the resulting cell eiiiuent as far aspracticable to sodium bicarbonate, increasing the precipitation ofcarbonate by adding more sodium chloride, filtering out the resultingprecipitated carbonation product, recycling the filtrate to the anodecompartment of the electrolytic cell, introducing -said carbonationproduct into an aqueous menstruum in quantity suiiicient to take intosolution at 50 to 70 C. most of the chlorate but only a little of thechloride which may be produced by chlorinating said carbonation product,chlorinating said carbonation product to produce the correspondingchlorate, recycling the resulting carbon dioxide to the carbonationstep, filtering out chloride and recycling it to the anode compartmentof the electrolytic cell, crystallizing out and removing chlorate fromthe filtrate, recycling the mother liquor to the chlorination step toserve as menstruum for said carbonation prodnot and introducing into thesystem make-up water and'chioride to supply the oxygen and chlorinewithdrawn from it with the product.

3. The process for production of sodium chlorate from electrolyticcaustic soda-chlorine cell eiiiuent with avoidance of evaporation ofwater therefrom which comprises electrolyzing sodium chloride in anelectrolytic cell, saturating the resulting cell emuent with sodiumchloride, carbonating said efliuent as far as practicable to sodiumbicarbonate, filtering out the resulting precipitated carbonationproduct, recycling the filtrate to the anode compartment of theelectrolytic cell, introducing said carbonation product into an aqueousmenstruum in quantity sufilcient to take into solution at 50 to 70 C.most of the chlorate but only a little of the chloride which may beproduced by chlorinating said carbonation product, chlorinating saidcarbonation product to produce the corresponding chlorate, recycling theresulting carbon dioxide to the carbonation step, filtering out chlorideand recycling it to the anode compartment of the electrolytic cell,crystallizing out and removing chlorate from the filtrate, recycling themother liquor to the chlorination step to serve as menstruum for saidcarbonation productv and introducing into the system make-up water andchloride to supply the oxygen and chlorine withdrawn from it with theproduct.

4. The process for production of sodium chlorate from electrolyticcaustic soda-chlorine cell eiiiuent with avoidance of evaporation ofwater therefrom which comprises electrolyzing sodium chloride in anelectrolytic cell, carbonating the resulting cell eil'iuent as far aspracticable to sodium bicarbonate, saturating said eiiiuent with sodiumchloride, filtering out the resulting precipitated carbonation product,recycling the filtrate to the anode compartment of the electrolyticcell, introducing said carbonation product into an aqueous menstruum inquantity suflicient to take into solution at 50 to 70 C. most of thechlorate but only a little of the chloride which may be produced bychlorinating said carbonation product, chlorinating said carbonationproduct to produce the corresponding chlorate, recycling the resultingcarbon dioxide to the carbonation step, filtering out chloride andrecycling it to the anode compartment of the electrolytic cell,crystallizing out and removing chlorate from the filtrate, recycling themother liquor to the chlorination step to serve as menstruum for saidcarbonation product and introducing into the system make-up water andchloride to supply the oxygen and chlorine withdrawn from it with theproduct.

5. The process for production of sodium chlorate from electrolyticcaustic soda-chlorine cell eiiiuent with avoidance of evaporation ofwater therefrom which comprises electrolyzing sodium chloride in anelectrolytic cell, carbonating the caustic alkali out of the resulting.cell eiiiuent as iaras practicable to sodium bicarbonate, filtering outthe resulting precipitated carbonation product, recycling the filtrateto the anode compartment of the electrolytic cell, introducing saidcarbonation product into an aqueous menstruum in quantity sufiicient totake into solution at 50 to 70 C. most of the chlorate but only a littleof the chloride which may be produced by chlorinating said carbonationproduct, chlorinating said carbonation product to produce thecorresponding chlorate, condensing and removing water from the resultingcarbon dioxide and recycling the carbon dioxide to the carbonation step,filtering out chloride, washing said chloride and recycling it to theanode compartment of the electrolytic cell, crystallizing chlorate outof the filtrate, washing the crytsals while balancing the quantity ofwater introduced in this and the previous washing of the chlorideagainst the quantity removed from the carbon dioxide, recycling themother liquor to the chlorination step to serve as menstruum for saidcarbonation product and introducing into the system make-up water andchloride to supply the oxygen and chlorine withdrawn from it with theproduct.

6. The process for production of potassium chlorate from electrolyticcaustic soda-chlorine cell eflluent with avoidance of evaporation ofwater therefrom which comprises electrolyzing sodium chloride in anelectrolytic cell, carbonating the caustic soda out of the resultingcell eflluent as far as practicable to sodium bicarbonate, filtering outthe resulting precipitated carbonation product, recycling the filtrateto the anode compartment of the electrolytic cell, introducing saidcarbonation product into an aqueous menstruum in quantity sufiicient totake into solution at 50 to 70 C. most of the chlorate but only a littleof the chloride which may be produced by chlorinating said carbonationproduct, chlorinating said carbonation product to produce'thecorresponding chlorate, recycling the resulting carbon dioxide to thecarbonation step, reacting the resulting chlorate with potassiumchloride in quantity slightly less than sufficient to convert all of itto potassium chlorate, filtering out chloride and recycling it to theanode compartment of the electrolytic cell, crystallizing out andremoving potassium chlorate from the filtrate, recycling the motherliquor to the chlorination step to serve' as menstruum for saidcarbonation product and introducing to the system water to supply theoxygen withdrawn from it with the product.

7. The process for production of sodium chlorate from electrolyticcaustic soda-chlorinecell eifluent with avoidance of evaporation ofwater therefrom which comprises electrolyzing sodium chloride in anelectrolytic cell, carbonating the caustic alkali out of the resultingcell efliuent as as far as practicable to sodium bicarbonate, filteringout the resulting precipitated carbonation product, recycling thefiltrate to the anode compartment of the electrolytic cell, introducingsaid carbonation product by increment into an aqueous menstruum inquantity sufficient to take into solution at 50 to 70 most of thechlorate but only a little of the chloride which may be produced bychlorinating said carbonation product, substantially completelychlorinating each increment of carbonation product, to produce thecorresponding chlorate, so that thickening and foaming are controlled,recycling the resulting carbon dioxide to the carbonation step,filtering out chloride and recycling it to the anode compartment of theelectrolytic cell, crystallizing out and removing chlorate from thefiltrate, recycling the mother liquor to the chlorination step to serveas menstruum for said carbonation product and introducing into thesystem make-up water and chloride to supply the oxygen and chlorinewithdrawn from it with the product. v

8. In the production of sodium chlorate the steps which compriseintroducing a carbonation product of caustic soda by increments into anaqueous menstruum, substantially completely :rhlorinating each incrementof carbonation product to produce the corresponding chlorate, so thatthickening and foaming are controlled, continuing the addition andchlorination of carbonation product by increments until an amount ofcarbonation product equivalent to substantially 240 grams of sodiumcarbonate has been added per liter of menstruum, filtering out chloride,crystallizing out chlorate from the filtrate and recycling the motherliquor from the crystallization step to the chlorination step to serveas a menstruum for said carbonation product.

9. In the production of sodium chlorate the steps which compriseintroducing a carbonation product of caustic soda by increments into anaqueous menstruum, substantially completely chlorinating each incrementof carbonation product to produce the corresponding chlorate, so thatthickening and foaming are controlled, continuing the addition andchlorination of carbonation product by increments until an amount ofcarbonation product equivalent to substantially 240 grams of sodiumcarbonate has been added per liter of menstruum, filtering out chloride,crystallizing out chlorate from the filtrate, washing the crystals andrecycling the mother liquor from the crystallization step and the washwater from the washing step to serve as a menstruum for said carbonationproduct.

10. In the production of sodium chlorate the steps which compriseintroducing sodium carbonate by increments into an aqueous menstruum,substantially completely chlorinating each increment of carbonate toproduce the corresponding chlorate, so that thickening is controlled,continuing the addition and chlorination of sodium carbonate byincrements until substantially 240 grams have been added per liter ofmenstruum, filtering out chloride, crystallizing out chlorate from thefiltrate and recycling the mother liquor from the crystallization stepto serve as a menstruum for said carbonate.

11. In the production of sodium chlorate the steps which compriseintroducing sodium bicarbonate by increments into an aqueous menstruum,substantially completely chlorinating each increment of bicarbonate toproduce the corresponding chlorate, so that foaming is controlled,continuing the addition and chlorination of sodium bicarbonate until anamount equivalent to substantially 240 grams of sodium carbonate hasbeen added per liter of menstruum, filtering out chloride, crystallizingout chlorate from the filtrate and recycling the mother liquor from thecrystallization step to serve as a menstruum for said bicarbonate.

12. The process for production of sodium chlorate from electrolyticcaustic soda-chlorine cell eilluent with avoidance of evaporation ofwater therefrom which comprises electrolyzing sodium chloride in anelectrolytic cell, saturating the resulting cell eflluent by addingsodium chloride thereto, carbonating the caustic soda out of saideflluent, under a slight pressure, as far as practicable to sodiumbicarbonate, with a yield of precipitated bicarbonate above 90 percentof the theoretical yield thereof, filtering out the resultingprecipitated bicarbonate, recycling the filtrate to the anodecompartment of the electrolytic cell, introducing the precipitatedbicarbonate into an aqueous menstruum in quantity suflicient to takeinto solution at 50 to 70 C. most of the chlorate but only a little ofthe chloride which may be produced by chlorinating said bicarbonate,chlorinating said bicarbonate to produce the corresponding chlorate,recycling the resulting carbon dioxide to the carbonation step,filtering out chloride and recycling it to the anode compartment or theelectrolytic cell, crystallizing out and removing chlorate from thefiltrate, recycling the mother liquor to the chlorination step to serveas menstruum for said bicarbonate and introducing into the system makeupwater and chloride to supply the oxygen and chlorine withdrawn from itwith the product.

13. The process for production of potassium chlorate from electrolyticcaustic soda-chlorine cell eiiluent with avoidance of evaporation ofwater therefrom and with an overall yield thereof above 80 per centwhich comprises electrolyzing sodium chloride in an electrolytic cell,saturating the resulting cell eflluent by adding sodium chloridethereto, carbonating the caustic soda out of said eiiluent as far aspracticable to sodium bicarbonate, under a slight pressure, filteringout the resulting precipitated bicarbonate, recycling the filtrate tothe anode compartment of the electrolytic cell, introducing theprecipitated bicarbonate into an aqueous menstruum in quantitysufllcient to take into solution at 50 to 70 C. most of the chlorate butonly a little of chloride which may be produced by chlorinating saidbicarbonate, chlorinating said bicarbonate to produce thecorrespondingchlorate, condensing and removing water from the resulting carbondioxide and recycling the carbon dioxide to the carbonation step,reacting the resulting chlorate with potassium chloride in quantityslightly less than sufiicient to convert all of it to potassiumchlorate, filtering out the chloride, washing said chloride andrecycling it to the anode compartment of the electrolytic cell,crystallizing out and removing the potassium chlorate from the filtrate,washing the chlorate troducing into the system water to supply theoxygen withdrawn from it with the product.

14. The process for production of sodium chlorate from electrolyticcaustic soda-chlorine cell eflluent with avoidance of evaporation ofwater therefrom, which comprises electrolyzing sodium chloride in anelectrolytic cell, carbonating the caustic alkali out of the resultingeflluent as far as practicable to sodium bicarbonate, filtering out theresulting carbonation product, recycling the filtrate to the anodecompartment of the electrolytic cell, chlorinating said carbonationproduct to the corresponding chlorate, filtering out chloride andrecycling it to the anode compartment of the electrolytic cell andremoving the chlorate from the filtrate.

15. The process for production of sodium chlorate from electrolyticcaustic soda-chlorine cell eiiluent with avoidance of evaporation ofwater therefrom, which comprises electrolyzing sodium chloride in anelectrolytic cell, carbonating the caustic alkali out of the resultingefiluent as far as practicable to sodium bicarbonate, filtering out theresulting precipitated carbonation product, introducing said carbonationproduct into an aqueous menstruum in quantity sufilcient to take intosolution most of the chlorate but only a little or the chloridewhich maybe produced by chlorinating said carbonation product, chlorinating saidcarbonation product to the corresponding chlorate, recycling theresulting carbon dixoide to the carbonation step, filtering out chlorideand recycling it to the anode compartment of the electrolytic cell,crystallizing out and removing chlorate from the filtrate, recycling themother liquor to the chlorination step to serve as menstruum for saidcarbonation product and introducing into the system make-up water andchloride to supply the oxygen and chlorine withdrawn from it with theproduct.

SIDNEY G. OSBORNE.

ROBERT B. LOWRY.

WALTER S. BEANBLOSSOM.

